Insect Pests of Crape Myrtles and Suggestions for Their Control

Transcription

1 Insect Pests of Crape Myrtles and Suggestions for Their Control Kimberly Engler Program Specialist-Urban IPM Texas Cooperative Extension Crape myrtles are very popular plants among Southern gardeners, due to their beauty and low maintenance requirements. The ideal planting sites for crape myrtles are in well-prepared, welldrained soils at locations with full sun exposure and good air circulation. These conditions will ensure the growth of healthy trees. A stressed tree is more susceptible to damage by insects and disease. The major insect pests of crape myrtles in Texas are crape myrtle aphids, Japanese beetles, and primrose flea beetles. A few insects on a plant usually do not cause damage to the plant. However treatment may be necessary to prevent further damage, if an insect population increases. Treatment options may include both non-chemical and chemical practices. Chemical insecticide application should be used as a last resort and wherever possible the least toxic, most target-specific insecticide should be applied. The crape myrtle aphid, Tinocallis kahawaluokalani Kirkaldy, has a narrow host range and is the only aphid species that feeds on crape myrtles. Crape myrtle aphids are found from May through September, with peak populations during July and early August. Crape myrtle aphid adults and nymphs are pale yellow-green with black spots on their abdomens and range from 1 /16 to 1 /8 inch in length. These aphids generally feed on the underside of crape myrtle leaves. They feed by inserting their needle-like mouthparts into the soft tissue and extracting plant sap. As aphids feed, they inject saliva into the leaf tissue which causes yellow leaf spots to develop. Heavy infestations can deform leaves and stunt new growth. Buds, branch tips and flowers can also be damaged by feeding injury. In addition to direct damage, aphids can damage plants indirectly by secreting honeydew, a sugary bi-product of their feeding. Honeydew is a perfect substrate for the growth of sooty mold fungi and a source of food for other insects such as ants, wasps and flies. Although unsightly, sooty mold itself does not directly harm the crape myrtle; instead it shades the leaves from light and interferes with photosynthesis. Under heavy infestations, sooty mold-covered leaves may drop early. The Japanese beetle, Popillia japonica Newman, was introduced into New Jersey in It spread throughout the eastern U.S. and then into the southern states. It is 1/3 to ½ inch in length and broad oval in shape. Its wings are coppery in color with fine longitudinal lines, and its body is a beautiful metallic green. It has five tufts of white hairs projecting from under the front wing on each side, with two patches of white hairs at the tip of the abdomen.

2 Both adults and larvae can damage the crape myrtles. The larvae live underground where they usually feed on roots of grasses, but may consume young tree roots. The adults prefer to eat the tissue between the leaf veins, causing a lacelike appearance. Adults are most active during the warmest part of the day and they are usually found on trees that are in full sun. The primrose flea beetle, Altica litigata Fall, is ¼ inch in length, oval in shape, and shiny bluegreen in color. All the immature lifestages of a flea beetle occur underground, so only the adults are seen by gardeners. The adult beetles lay their eggs and the larvae feed on the roots of primroses, Ludwigia. However, the larvae can feed on the foliage or tunnel into the plant stems. Adults feed on crape myrtle, evening primrose and other plants, although the normal host is Ludwigia. T he adult beetles will chew many holes or pits into the leaves, leaving shot holes in the leaves. The effect of their feeding is most severe when they attack the growing tips, because this limits the ability of the plant to compensate for damage, making young plants and seedlings particularly susceptible. As a result, growth may be reduced or the plant may die. Preserving Natural Enemies and Some Non-Chemical Control Suggestions: Insect Pests Crape Myrtle Aphids Japanese Beetles Primrose Flea Beetleo Preserve Natural Enemies Lady bugs, lacewings, syrphid and hover fly larvae; birds such as finches, mockingbirds, woodpeckers Wheel bugs, robber flies and praying mantids; birds such as crows, starlings, song sparrows, robins and grackles Big-eyed bugs, larvae of green lacewings, damsel bugs and field crickets Physical/Mechanical Control Hand picking, clip or pinch off plant tips and discard them in the trash. Hand picking; removing and destroying infested branches High Pressure Water Spray Use a nozzle attachment or a high pressure sprayer. Repeat regularly to gain control Remove Weeds Remove weeds in and around planting sites to deprive larvae of food sources Chemical Control Suggestions*: Insect pest Crape Myrtle Aphids Recommendations Insecticidal Soaps and Horticultural Oil, Neem Oil (organics); Acephate, Permethrin, Deltamethrin, Imidacloprid, Cyfluthrin, Bifenthrin (synthetics)

3 Japanese Beetle Primrose Flea Beetle Neem oil, Roteneone, Azadirachtin (organics); Acephate, Bifenthrin, Permethrin, Lambda-cyhalothrin, Cyfluthrin, Deltamethrin, Carbaryl, Imidacloprid (synthetics) Neem oil, Rotenone, Azadirachtin, Spinosad (organics); Carbaryl, Bifenthrin, Cyfluthrin, Deltamethrin (synthetics) *Listed are active ingredients found in various products. Mention of commercial products is for educational purposes only and does not represent endorsement by Texas Cooperative Extension or The Texas A&M University System. Insecticide label registrations are subject to change, and changes may have occurred since this publication was printed. The pesticide user is always responsible for applying products in accordance with label directions. Always read and carefully follow the instructions on the container label. Crape Myrtle Aphid

4 Japanese Beetle Primrose Flea Beetle

5 Primrose Flea Beetle Damage